The present invention relates to an integrated optoelectronic sensor of a measuring system for scanning a scale with graduation markings, and to a method for manufacturing such sensor.
British Patent 1,504,691 and a corresponding German Patent Application 25 11 350 A1 describe a measuring system in which the movement of a first assembly relative to a second assembly is detected. For this purpose, there are two gratings, which are at a constant distance from each other, each being attached to one assembly, When the second grating is illuminated by the divergent light of a light source, the first grating generates a periodic image of the second grating. The image is not stationary if there is a relative motion between the two assemblies.
Photo detectors are also included, which have a periodic pattern and are fixedly joined to the second assembly. The first grating is a reflecting grating, and the second grating as well as the photo detectors are essentially in the same plane. The light source and the second grating can also be replaced by a pattern-generating light source, which generates the same image as would a conventional light source and a grating. The pattern of the photo detectors interacts with the image such that a periodic change of the output signal of the photo detectors occurs if there is a relative movement between the first and second assemblies.
One are disadvantage of this system is that the two assemblies are formed individually, separately from one another. As a result, a relatively large space is required to assemble the entire arrangement.
German Patent Application 197 01 941 A1, describes arranging a scanning grating on the side of a light-transmissive carrier that is facing a scale. The scanning grating is illuminated by a light source such that an image of the grating is projected onto the scale. A second grating is located on the scale, which reflects the image onto a pattern-generating photo detector. The light-transmissive carrier for the first grating is connected to the semiconductor material in which the pattern-generating photo detector is formed, so that the scanning grating and the photo detector are shifted exclusively in the measuring direction with respect to each other. The scanning grating and photo detector are at the same distance from the scale. German Patent Application 197 01 941 A1 also describes a scanning grating arranged on the side of the light-transmissive carrier that is facing away from the scale. An optical chip is arranged on the same light-transmissive carrier that contains the photo detector, on the same side as the scanning grating. This arrangement makes it possible to place the scanning grating and the pattern-generating photo detector at approximately the same distance from the scale.
The described system has the disadvantage that the light-transmissive carrier, on which the scanning grating is applied, must be joined to the semiconductor material in which the pattern-generating photo detector is formed. This connection must be carried out very precisely so that the pattern of the photo detector is aligned parallel to the grating, and the pattern and the grating have the same distance from the scale, This exact connection between carrier and semiconductor material is therefore very difficult to form.
The system also has the disadvantage that an optical chip has to be secured on the light-transmissive carrier. By securing the chip using chip-on-glass technology, it is inevitable that a distance will exist between the optical chip and the carrier. Because of this arrangement, the distances between the scanning grating and the scale, and between the photo detector and the scale significantly deviate from each other, which leads to a significant degradation of the optical properties of the arrangement.
German Patent 40 91 517 T1, describes a sensor for a measuring system made from a single block of semiconductor material. On the surface of a planar-configured light-emitting diode, there are photo elements configured as grating lines, through which the light-emitting diode can shine. In this way, a pattern-generating photo detector is formed, above or below which a pattern-generating light source is arranged.
One disadvantage of this sensor is that the photo detector pattern and the pattern-generating light source cannot have the same distance from a scale, since the light-emitting diode and the photo detector are disposed on top of each other. This varying distance to the scale in turn impairs the optical properties of the sensor.
European Patent Application 543 513 A1, describes a common semiconductor substrate made of III/V semiconductor material, such as gallium arsenide GaAs, having both a pattern-generating photo detector as well as a pattern-generating light source. Both of these components can be formed by a light-emitting diode and a sensor. By forming the pattern-generating light source and the pattern-generating photo detector on a common semiconductor material, the transmitting and receiving structuring can easily be placed as closely as possible in the same plane. Furthermore, a single-field scanning takes place in which the photo elements are shifted by [90xc2x0+(k*360)] degrees, with k being an integer. Therefore, a plurality of photo elements can be arranged so as to be shifted with respect to each other, in the measuring direction, by ninety degrees of angle plus whole-number multiples of three hundred sixty degrees of angle. In this ways the scanning becomes particularly insensitive to disturbances.
A disadvantage of this design is that there is no description how the pattern-generating photo detector and the pattern-generating light source can be manufactured on a common semiconductor material made of GaAs. If known technologies of semiconductor manufacturing from the related art are applied, this manufacturing process is very cumbersome and therefore expensive.
European Patent Application 720 005 A2 describes an optical sensor for a measuring system, which has a light-emitting component, a light-receiving component, and at least one optical component, which influences the beam of light emitted by the light-emitting component before the beam of light reaches the light-receiving component. This sensor has a distancing element, which defines a distance between the light-emitting or the light-receiving component and the optical component. According to the design, the optical sensor emits and receives optical signals on its side, so that all optical assemblies are arranged on the same side, and the leads for electrical signals are on the opposite side of the sensor.
One disadvantage of this system is that the light-receiving component, the light-emitting component, the at least one optical component, and the distancing element are all made as separate components, which must be manufactured and assembled separately. In view of the required tolerances for optical sensors of measuring systems, this process is very expensive. Furthermore, the optical sensor is relatively bulky, because the individual components must also be manipulated separately.
German Patent Application 197 20 300 A1 describes an electronic hybrid structural component with a chip-on-chip arrangement, where an implanted chip is arranged on a carrier substrate. For this purpose, the carrier substrate has at least one cavity in which is located an electrical insulating layer having a metallic layer on top of it. The chip implanted in the cavity contacts the metallic layer, as a result of which the latter is used as an electrical lead. If the implanted chip is a light-emitting diode, the metallization layer can also be used to reflect its beam on the walls of the cavity.
This arrangement has the disadvantage that both the illuminating direction of the light-emitting diode as well as its electrical contacts are arranged on one side of the semiconductor substrate, and light is only emitted on this one side.
German Patent Application 196 18 593 A1 describes a photo-sensitive detector element having an active region, the active region being configured between two adjoining layer areas of a layered arrangement, having differing charge carriers and within which an incident electromagnetic beam is converted into electrical signals. The position of the active region relative to the two adjoining surfaces is selected, taking into account the penetration depth of the beam, such that at least two contact elements can be mounted. The two contact elements form a connection of the detector element with an evaluation circuit on a surface which is situated opposite the photo-sensitive surface onto which the incident beam arrives.
In the manufacturing process of a detector element of this type, the following process steps are employed. A semiconductor substrate is doped to a defined extent, and an etching stop layer is generated immediately beneath a limiting first surface. A spatially selective etching away of the substrate present beneath the etching stop layer then takes place, until the etching stop layer forms a limiting second surface. Subsequently, a spatially limited layer area above the etching stop layer, having a different doping than the semiconductor substrate, is generated. The detector element contacts at least two contact elements on a side that is opposite the second surface. However, this document only discloses a photo diode, but no complete optoelectronic sensor is described.
There is thus a need for an integrated optoelectronic sensor and a method to manufacture it, in which the components of the sensor are formed in an integrated manner on a semiconductor substrate. Preferably, all of the electrical contacts are placed on one side of the semiconductor substrate, and all of the optical signals are emitted and received on the other side. The manufacturing process for this integrated optoelectronic sensor is also more cost-effective than current processes.
The system according to the present invention has a light source, photo elements, and an intensifier as well as an interpolation unit that can be integrated on one semiconductor substrate. All electrical contacts of the components of the sensor are arranged on the side of the sensor facing away from the scale, while the optical signals are emitted and received on the side of the sensor facing the scale. The small size of the assembly and the high degree of integration lead to reduced manufacturing costs. the optoelectronic chip having photo elements, light source, and evaluation electronics can be joined to the carrier for the scanning grating in a simple manner.